This invention relates to cooling arrangements for semiconductor devices, and more particularly to cooling arrangements using circulating fluid coolant.
The history of communications and of computing is a continuing saga of increasing power densities as increased transmitted power is sought in conjunction with shorter and shorter wavelengths, and as the path lengths in microprocessors are reduced in conjunction with increasing numbers of processing elements.
In the field of communications and radar, it is desirable to reduce the cost, size, and weight of antennas. In general, antenna gain is a function of its size measured in wavelengths, so that, at a given frequency, antenna gain decreases as antenna size decreases. A corollary is that antenna the gain of a physically small antenna may be increased by increasing the operating frequency. In an array antenna, the inter-element spacing decreases as the operating frequency increases. In general, the effective range of a radar or communication system depends upon how much power can be transmitted toward the target or receiver, since the designers of radar and communications systems attempt to use the best transistors or other signal amplifiers, namely those capable of transmitting the highest power, and for reception, those providing the lowest noise.
In an array antenna associated with a ground plane, the interelement spacing of the radiating elements defines the area behind the ground plane which can be devoted to electronics associated with a particular antenna element. The drive toward smaller antennas tends to result in higher frequencies, at which electronic equipment tends to be less efficient that at lower frequencies. Thus, array antennas for modern systems tend to operate at high frequencies and high power, with small antenna inter-element spacing. This, in turn, means a tendency toward higher power dissipation in the associated equipment. U.S. Pat. No. 5,013,997, issued May 7, 1991 in the name of Reese, describes a phase shifter for an array antenna in which a ferrite phase shifter coupled directly to the horn antenna element is immersed in liquid, and the hot liquid is made available to the radome for deicing. Other systems, such as that described in U.S. Pat. No. 5,017,927, issued May 21, 1991 in the name of Agrawal et al., make use of transmit-receive (TR) modules using one module associated with each antenna element. These TR modules include phase shifters, power amplifiers, low-noise amplifiers, and various types of filtering. In such an arrangement, the high frequency operation and high power results in large heat generation by transmitting transistors associated with each antenna element TR module, coupled with relatively small spacing between adjacent ones of the modules.
The performance of transistors and solid-state devices is closely linked to the operating temperature, and the reliability of such transistors and solid-state devices is linked to the long-term or historic operating temperature. Both of these considerations require keeping operating temperatures as low as possible. In the context of the high packing densities of array antennas, maintaining a low temperature of at least some portions of a transmitter is a significant problem.
Various options present themselves, such as reducing the heat generated so that conventional thermal conduction suffices. However, this tends to reduce the electromagnetic signal power available for transmission. If the amount of heat is given as a constant, other techniques can be used, such as cooling air flow in conjunction with finned heat sinks for the transistors or other solid-state devices, thermal management materials having extremely low thermal impedance, heat pipes, and liquid-filled cold plates. The problem of temperature control is much exacerbated by the need to make all the antenna element modules identical to reduce the manufacturing cost, and the need for such modules to be field-interchangeable. In the context of computer microprocessors, the drivers are the need for increased numbers of logic elements within confines which maintain short signal path lengths for high-speed operation.
U.S. Pat. No. 5,999,407, issued Dec. 7, 1999 in the name of Meschter et al. describes a scheme for conductively heat-sinking a heat-generating device mounted on a printed-circuit board through a thermally conductive structure to a module mounting rail, and thence to an ultimate heat sink. U.S. Pat. No. 5,552,633, issued Sep. 3, 1996 in the name of Sharma, describes the transfer of heat in a multilayer interconnect structure by way of thermally conductive posts extending through the multilayer structure. U.S. Pat. No. 5,459,474 issued Oct. 17, 1995 in the name of Mattioli et al. describes an active array antenna in which the antenna element modules, together with portions of the elemental antennas themselves, are mounted in side-by-side racks which slide from their operating position for maintenance.
Improved solid-state device cooling is desired for removable modules in closely spaced arrays and for chips having a high elemental packing density.
In the most general terms, a cooling arrangement according to various aspects of the invention is useful for semiconductors or solid-state assemblages which mount the semiconductor or other solid-state device directly onto a first surface of a thermally conductive xe2x80x9cheat spreader.xe2x80x9d The heat spreader contains microchannels which open into coolant fluid ports on the second side of the heat spreader. The heat spreader, in turn, is mounted on a coolant fluid distribution or circulation plate. In one embodiment, the coolant fluid distribution plate also includes a micropump for circulating coolant fluid through the microchannels of the heat spreader. In another embodiment, the coolant fluid distribution plate simply distributes coolant applied to its fluid input port to those heat spreaders mounted thereon, and a plurality of coolant fluid distribution plates are mounted on a coolant fluid circulation plate, which uses a micropump to circulate coolant fluid to the various distribution plates and ultimately to the heat spreaders. Thus, coolant fluid is communicated directly into the support for the semiconductor chip or other solid-state device, for good heat transfer with low temperature drop.
In another general aspect of the invention, a solid-state device, such as, for example, a transistor, a laser, phase shifter or the like, is mounted on a supporting thermally conductive piece. The piece on which the solid-state device is mounted contains microchannels through which a flow of coolant fluid is established. The coolant flow originates, in a preferred embodiment of the invention, with a xe2x80x9ccoldxe2x80x9d plate to which the thermally conductive piece is mounted, and in which a micropump causes coolant fluid to circulate.
More particularly, a monolithic solid-state chip includes a planar dielectric substrate defining first and second broad surfaces. For purposes of this invention, the planar dielectric substrate may include a semiconductor substrate which is not doped, or doped so as to be relatively nonconductive. The solid-state chip also defines electrical conductors lying on the first surface. The solid state chip produces heat during operation. According to an aspect of the invention, a thermally conductive plate including a first broad surface is directly connected to the second surface of the solid-state chip. The thermally conductive plate also includes a second broad surface substantially parallel with the first broad surface, at least sufficiently for mounting convenience. The thermally conductive plate includes at least one microchannel extending between coolant fluid input and output ports and between the first and second broad surfaces of the thermally conductive plate. The microchannel has a cross-sectional area smaller than about 0.001 square inch. In a preferred embodiment, the coolant fluid input and output ports are located on the second broad surface of the thermally conductive plate, and the microchannel is branched or formed into a finned structure at locations under the planar dielectric substrate, to increase the rate of heat exchange. A source of pressurized coolant fluid is coupled to the input port of the thermally conductive plate. In a particular version, the source of pressurized fluid coolant includes a micropump. One version of the micropump is operated by electric fields rather than magnetic fields. In another version, the micropump has a thickness less than about {fraction (2/10)} inch.
Another avatar of the invention lies in an array of electronic devices. The array comprises (a) a first monolithic solid-state chip including a planar dielectric substrate defining first and second broad surfaces, and also defining electrical conductors lying on the first surface. The first monolithic solid state chip producing heat during operation. The array also comprises (b) a first thermally conductive plate including a first broad surface directly connected to the second surface of the first solid-state chip. The first thermally conductive plate also includes a second broad surface substantially parallel with the first broad surface. The first thermally conductive plate includes at least one microchannel extending between coolant fluid input and output ports lying on the second broad surface of the first thermally conductive plate and between the first and second broad surfaces of the first thermally conductive plate. The microchannel has a cross-sectional area smaller than about 0.001 square inch. The array further comprises (c) a second monolithic solid-state chip including a planar dielectric substrate defining first and second broad surfaces, and also defining electrical conductors lying on the first surface. The second monolithic solid state chip produces heat during operation. The array further includes (d) a second thermally conductive plate including a first broad surface directly connected to the second surface of the second solid-state chip, and also including a second broad surface substantially parallel with the first broad surface. The second thermally conductive plate includes at least one microchannel extending between coolant fluid input and output ports lying on the second broad surface of the first thermally conductive plate and between the first and second broad surfaces of the second thermally conductive plate. The microchannel has a cross-sectional area smaller than about 0.001. (e) A third planar structure is provided. The third planar structure includes a broad first surface defining at least first, second, third and fourth fluid ports, the first and second fluid ports being registered with and immediately coupled to the fluid input and output ports of the first thermally conductive plate, and the third and fourth fluid ports being registered with and immediately coupled to the fluid input and output ports of the second thermally conductive plate, so that the second planar surfaces of the first and second thermally conductive plates. The third planar structure further defines a closed fluid path extending among the first, second, third and fourth fluid ports. The third planar structure further includes a micropump contained between the first and second broad surfaces of the third planar structure and coupled to the closed fluid path, for, when in operation, circulating coolant fluid through the closed fluid path to the coolant fluid input ports of the first and second thermally conductive plates, and from the coolant fluid output ports of the first and second thermally conductive plates.
According to another manifestation or aspect of the invention, an array of electronic devices includes a first and a second module, first and second intermediate fluid distribution plates, and a common fluid circulating plate. The first module comprises (a) a first monolithic solid-state chip including a planar dielectric substrate defining first and second broad surfaces, and also defining electrical conductors lying on the first surface. The first solid state chip produces heat during operation. The first module also includes (b) a first thermally conductive plate including a first broad surface directly connected to the second surface of the first solid-state chip, and also includes a second broad surface substantially parallel with the first broad surface. The first thermally conductive plate includes at least one microchannel extending between coolant fluid input and output ports lying on the second broad surface of the first thermally conductive plate and extends between the first and second broad surfaces of the thermally conductive plate. The microchannel has a cross-sectional area smaller than about 0.001 square inch, but may branch into plural parallel microchannels for enhancing heat transfer. The first module further includes (c) a second monolithic solid-state chip including a planar dielectric substrate defining first and second broad surfaces, and also defining electrical conductors lying on the first surface. This second solid state chip also produces heat during operation. The first module includes (d) a second thermally conductive plate including a first broad surface directly connected to the second surface of the second solid-state chip, and also including a second broad surface substantially parallel with the first broad surface. The second thermally conductive plate includes at least one microchannel extending between coolant fluid input and output ports lying on the second broad surface of the first thermally conductive plate and between the first and second broad surfaces of the second thermally conductive plate. The microchannel has a cross-sectional area smaller than about 0.001 square inch. The second module comprises (a) a first monolithic solid-state chip including a planar dielectric substrate defining first and second broad surfaces, and also defining electrical conductors lying on the first surface. The first solid state chip of the second module produces heat during operation. The second module includes (b) a first thermally conductive plate including a first broad surface directly connected to the second surface of the first solid-state chip, and also including a second broad surface substantially parallel with the first broad surface. The first thermally conductive plate includes at least one microchannel extending between coolant fluid input and output ports lying on the second broad surface of the first thermally conductive plate and between the first and second broad surfaces of the thermally conductive plate; the microchannel has a cross-sectional area smaller than about 0.001 square inch. The second module also includes (c) a second monolithic solid-state chip including a planar dielectric substrate defining first and second broad surfaces, and also defining electrical conductors lying on the first surface. As with the other solid-state chips, the second solid state chip of the second module produces heat during operation. The second module further includes (d) a second thermally conductive plate including a first broad surface directly connected to the second surface of the second solid-state chip, and also including a second broad surface substantially parallel with the first broad surface. The second thermally conductive plate of the second module includes at least one microchannel extending between coolant fluid input and output ports lying on the second broad surface of the first thermally conductive plate of the second module and between the first and second broad surfaces of the thermally conductive plate. As with the other microchannels, the cross-sectional area is smaller than about 0.001 square inch. The array of electronic devices also includes a first intermediate fluid distribution plate associated with the first module. The first intermediate fluid distribution plate defines a first broad side and a second broad side. The first intermediate fluid distribution plate includes at least one fluid input port and at least one fluid output port defined on the second broad side, and at least first, second, third and fourth fluid ports on the first broad side. The first and second fluid ports of the first intermediate fluid distribution plate of the array of electronic devices are registered with the fluid coolant input and output ports of the first thermally conductive plate of the first module, and the third and fourth fluid ports of the first intermediate fluid distribution plate are registered with the fluid coolant input and output ports of the second thermally conductive plate of the first module. The first intermediate fluid distribution plate distributes fluid entering the fluid input port of the first intermediate fluid distribution plate to the fluid coolant input ports of the first and second thermally conductive plates of the first module. The second intermediate fluid distribution plate is associated with the second module. The second intermediate fluid distribution plate is similar to the first, and defines a first broad side and a second broad side. The second intermediate fluid distribution plate includes at least one fluid input port and at least one fluid output port defined on the second broad side, and also defines at least first, second, third and fourth fluid ports on the first broad side thereof. The first and second fluid ports of the second intermediate fluid distribution plate are registered with the fluid coolant input and output ports of the first thermally conductive plate of the second module, and the third and fourth fluid ports of the second intermediate fluid distribution plate are registered with the fluid coolant input and output ports of the second thermally conductive plate of the second module, for distributing fluid entering the fluid input port of the second intermediate fluid distribution plate to the fluid coolant input ports of the first and second thermally conductive plates of the second module. Finally, the array of electronic devices includes a common planar fluid circulating plate. The common planar fluid circulating plate defines first and second broad surfaces. The first broad surface of the common planar fluid circulating plate defines at least first, second, third and fourth fluid ports. The first and second fluid ports of the common planar fluid circulating plate are registered with the fluid input and fluid output ports defined in the second broad side of the first intermediate fluid distribution plate, and the third and fourth fluid ports of the common planar fluid circulating plate are registered with the fluid input and output ports defined in the second broad side of the second intermediate fluid distribution plate. The common planar fluid circulating plate further comprises at least one fluid channel coupled to the first, second, third, and fourth fluid ports defined in the first side, and a micropump lying between the first and second broad sides of the common planar fluid circulating plate, for circulating fluid through the at least one fluid channel. A mounting arrangement or means is coupled to the first and second thermally conductive plates of the first and second modules, to the first and second intermediate fluid distribution plates, and to the common planar fluid circulation plate, for physically connecting the first and second thermally conductive plates of the first and second modules, the first and second intermediate fluid distribution plates, and the common planar fluid circulation plate together, so that the microchannels of the first and second thermally conductive plates of the first module, the microchannels of the first and second thermally conductive plates of the second module, the ports of the first and second intermediate fluid distribution plates, and the at least one fluid channel of the common planar fluid circulation plate form a closed fluid path through which coolant fluid is recirculated by the micropump. Ideally, the second broad surfaces of the first and second conductive plates of the first and second modules are juxtaposed with the first broad surfaces of their respective intermediate fluid distribution plates, and the second surfaces of the intermediate fluid distribution plates are juxtaposed with the first broad surface of the common planar fluid circulating plate.